New CAA low power portable ADS-B device spec

[exfirepro]

How can it be a ADS-B transmitting device when it does not transmit ADS-B messages (PAW=P3i) and it uses a frequency in the public band?

Hi StevN,

My reading of it is that Bob is saying that ANY system which deliberately transmits positional information with the intention that this will be received and decoded by another device to tell that system it is 'here', technically fits the definition of 'Automatic Dependent Surveillance (by) Broadcast (of that positional information). We just normally presume the term to be exclusive to specific transmissions on 1090MHz. That being the case, I guess FLARM would also fall into Bob's definition too!

To pick up bryannortje's point,

I would guess that what the NATS Project Eva Team are interested in is to investigate compatibility of LPAT by testing how well (or otherwise) it is received and actionned by other ADS-B in systems such as PAW and FLARM (a positive marketing point), by average pilots in a variety of aircraft and where a transmitter IS present that there are no interference problems, though I may of course be far off the mark. I was thinking of registering to get involved but reading the bit in their script about '...pilots having to talk live  to HD video cameras as alerts are received...'  and the fact they presumably need to attend your airfield to fit the video cameras and oversee the trials, I have my doubts as to the level of interest a couple of flex wings up in Scotland would provide. I may still make them the offer though just to see what is going on. Certainly TRIG, which is a major part of all this are only a couple of miles from where I live and it's their transponder gear I use, so you never know.

Best regards all

Peter

[Moffrestorer]

Having reminded myself what the initials ADS-B actually mean, via Wikipedia I have to conclude that Bob D is correct in his assertion that PAW is indeed an ADS-B device. I had always associated the term with 1090 ES, in my own thoughts. (Incidentally, Bob, I congratulate you on your informative paper; there is a dearth of info regarding ADS-B that is readily available or understandable and I'm surprised that I had not seen it previously, it's like the subject is top-secret. Where is the repository of all info on this subject held?).

Nonetheless, I stand by my comments that CAP 1391 contains little that is relevant to PAW. How should Lee and the Team respond to it, if at all? PAW doesn't directly transmit on 1090 ES. Without a Mode S ES associated with the PAW there is NO 1090 output; with a transponder, it's the transponder that's handling the ES broadcast, presumably using something other than DF 18 because it's a real transponder with current approvals rather than a "pseudo transponder" specified by CAP 1391. ( PAW solely outputs NMEA as RS232 to provide the necessary GPS source).

Like FLARM/ POWERFLARM, PAW transmits and receives on a different frequency using a different protocol to that described in the CAP. FLARM has already received some kind of approval from EASA, and as Lee has pointed out, there could be mutual interoperability with FLARM if they deemed to publish their protocol in the interests of safety.

I too am very interested in safety. Our group invested in a Becker Mode S transponder in 2010 which I think?? /hope may have ES capability, though it's not easy to be sure from its documentation or design iterations. I am desperate to be able to connect it to an uncertified GPS source to more readily "Be Seen" but the firmware does not currently allow SDA to be set to zero so this is a non-starter. Becker say they will address the problem but to be honest, I'm not holding my breath!

[BobD]

Hi Bob D,

Are you trying to steal my identity ? 

Seriously, I wonder if it is possible for the Administrator to change one of our User Names, without losing the posts, to avoid confusion ?

As a longer standing member, I claim squatters rights 

BobD (no space)

[Admin]

Hi Bob D,

Are you trying to steal my identity ? 

Seriously, I wonder if it is possible for the Administrator to change one of our User Names, without losing the posts, to avoid confusion ?

As a longer standing member, I claim squatters rights 

BobD (no space)

Appeal upheld, "Bob D", I have altered your screen name. Please modify if new name is not suitable
Admin

[flying_john]

I have read on several posts that it is not permitted to have two devices that transmit on 1090Mhz in one aircraft installation. May I ask where this rule is written please.

I don't understand the technical reason either.

The Mode S transponder is an interogation led device, i.e it gets interogated on 1030mhz and replies on 1090Mhz.

The ES transmission occurs pseudo randomly on 1090 with the ADSB data.

Where is the conflict ?  Can they not co -exist. Is it a worry that the two transmissions ( on some occasions) may overlap?

[AlanB]

I have read on several posts that it is not permitted to have two devices that transmit on 1090Mhz in one aircraft installation. May I ask where this rule is written please.

I don't understand the technical reason either.

The Mode S transponder is an interogation led device, i.e it gets interogated on 1030mhz and replies on 1090Mhz.

The ES transmission occurs pseudo randomly on 1090 with the ADSB data.

Where is the conflict ?  Can they not co -exist. Is it a worry that the two transmissions ( on some occasions) may overlap?

Reading the now published CAA document I believe the following applies

There shall be only one device using the ICAO aircraft address therefore;

If you have an A/C transponder with a low powered ADS-B device then only the ADS-B device will be broadcasting the ICAO aircraft address. In my interpretation that means I could have both devices operating.

If you have a Modes-S transponder with no ES output the Mode-S device will also be transmitting the ICAO airactft address and therefore only one device can be used.

If you have a Mode-S transponder with ES and a GPS connected then you would not need a separate transmitter as you would already be broadcasting your position as an ADS-B output via the transponder.

That is my interpretation of the published documentation and effectively I am interpreting the published information that the ban is effective on using a 1090 ADS-B out device in conjunction with a conventional Mode-S transponder with no ES and a Mode-S ES transponder you would not need a separate ADS-B out device anyway.

I was assisting NATS and AOPA during the trails of the LPAT and we asked all volunteers to switch off their transponders at the request of the CAA and NATS to ensure no cross interference during the trial.

This is my interpretation and I have already raised this with the CAA conspicuity working group as a Member of the FASVIG Conspicuity working group for a clear understanding as it is creating a good deal of conversation and needs to be closed down.

As a former radar engineer I have a clear understanding of the issues and why it's essential that the data to ATC systems is not compromised especially where maintaining separation of traffic is required. However I also believe the issue can be addressed and a better picture provided.

You have to appreciate that these devices and the rules around their use are in their infancy hence questions like this will arise and therefore good positive feedback is necessary to clear these issues. I hope you will also response to the CAA consultation on the low powered ADS-B specification so they are recorded through that mechanism.

Hope this helps.

Alan

[flying_john]

Just a thought then....

My Mode S transponder has a switch that allows me to have Mode A-S, Mode A-C and Mode S. If I select Mode C (Actually Mode A and C) then I will no longer be sending my Hex and A/C I.D. Then I could switch on my LPAT and would also be sending my Mode S E.S data allowing much more information to be sent than with the Mode S on my Txpdr. I was wrong

Also - if the spec says "only one device using" then isnt that still the case when the Mode S transponder is sending its burst of data, it is "using" the i.d and then when the Lpat sends its millisecond(s) burst - it is then "Using". Ok, occasionally they may both transmit simultaneously and produce fruit but it wont be decypherable.

John

Reading the now published CAA document I believe the following applies

Have you a link or CAP number for this please.

[SteveHutt]

John,
See very first post on this thread.
Steve

[AlanB]

Just a thought then....

My Mode S transponder has a switch that allows me to have Mode A, Mode C and Mode S. If I select Mode C (Actually Mode A and C) then I will no longer be sending my Hex and A/C I.D. Then I could switch on my LPAT and would also be sending my Mode S E.S data allowing much more information to be sent than with the Mode S on my Txpdr.

Also - if the spec says "only one device using" then isnt that still the case when the Mode S transponder is sending its burst of data, it is "using" the i.d and then when the Lpat sends its millisecond(s) burst - it is then "Using". Ok, occasionally they may both transmit simultaneously and produce fruit but it wont be decypherable.

John

Reading the now published CAA document I believe the following applies

Have you a link or CAP number for this please.

As Steve has pointed out the first post in this thread points to the CAP document and the opportunity to comment.

My own transponder is either on or alt with no option to disable the Mode-S features. I would also suggest that disabling a perfectly good Mode-S transponder would remove the advantage of providing ATC with your aircraft Callsign which aids them contacting you either on receiving a service or using a listening squawk.

The Hex code in the Mode-S response aids correlation in the plot extractors and display software and having multiple transmissions from the same target must all be processed, see the CAP document explanation, increasing the amount of fruit and time to determine the correct target and position.

Mode-S is a means of reducing fruit on the frequency by allowing selective interrogation in high density target areas using the ICAO Hex code. Deselecting that feature means that only an All Call from the ground interrogator will get a response form an A/C transponder. That together with MonoPulse all provides a greater integrity of target reasonsolution and verification allowing the reduction of separation criteria in areas where Mode-S predominates. So there are many factors to consider in this debate - but it is a debate and currently only my opinion based on my knowledge and experience.

In my view if you have a Mode-S transponder then having the ES option enabled with a GPS output would be my preferred option as then I would only be concerned about having a device that is listening for other targets.

[DaveStyles]

This thread is seeming like a moot point to me.
PilotAware is most definitely not 1090 ADSB out.

All this talk of one device etc etc may be pertinent to whether LPAT is compatible with a transponder, but I fail to see how it is pertinent to PilotAware.

With PilotAware you can SEE any of these other ADSB devices, you can BE SEEN if you have a mode S transponder and you connect PilotAware to it to give ADSB out (or indeed any GPS, but what's the point in doing only that, you can't "SEE" if you just connect GPS to your transponder) and you can even BE SEEN and SEE other PilotAware users.

[AlanB]

This thread is seeming like a moot point to me.
PilotAware is most definitely not 1090 ADSB out.

All this talk of one device etc etc may be pertinent to whether LPAT is compatible with a transponder, but I fail to see how it is pertinent to PilotAware.

With PilotAware you can SEE any of these other ADSB devices, you can BE SEEN if you have a mode S transponder and you connect PilotAware to it to give ADSB out (or indeed any GPS, but what's the point in doing only that, you can't "SEE" if you just connect GPS to your transponder) and you can even BE SEEN and SEE other PilotAware users.

Nothing wrong with what you state.

As I have posted earlier the use of electronic conspicuity devices is going beyond the old PCAS and FLARM units and equivalent and is in its early stages.

There is a lot going on in the development of he standards headed by the CAA and sponsored by Europe through Project EVA and the start of this thread highlighted the CAA CAP Document for those wishing to read, and comment as they desire.

I suggest that as operators of small light aircraft we only have room and money for one device and therefore we want value for money in a device that provides maximum visibility of others in the airspace and provides the maximum visibility of us to others.

Users have a choice of devices and I have no allegiance to any.

[flying_john]

John,
See very first post on this thread.
Steve

My Mistake - I thought there was another document. I had read this and could not find the reference to not having two devices in the same aircraft with the same hex code programmed in.

It does say that:-
6.14 EC devices offer no interoperability with interrogative collision alerting systems since DF=18 squitters from non-transponder EC devices will not be monitored by such systems.

This equipment offers interoperability at varying levels across functional capabilities and ranges from Airborne Collision Avoidance System (ACAS) II and Mode S transponders, required for most commercial air transport aircraft operated in controlled airspace, to ACAS I, Traffic Advisory Systems (TAS) and Mode S transponders for aircraft that are not required to be equipped to the same level, but that are voluntarily equipped to improve surveillance capability and situational awareness.

I read that as the EC is operable at the same time as the Mode S transponder.

This thread is seeming like a moot point to me.
PilotAware is most definitely not 1090 ADSB out.

Maybe not but does concern PAW owners who have bought early Mode S with no ES - (I believe Garmin Owners).

Deselecting that feature means that only an All Call from the ground interrogator will get a response form an A/C transponder. -

But they will have ES so will already be broadcasting their position, Altitude, possible speed, Velocity and so on - so they would not require interogating.

The Hex code in the Mode-S response aids correlation in the plot extractors and display software and having multiple transmissions from the same target must all be processed, see the CAP document explanation, increasing the amount of fruit and time to determine the correct target and position.

But in the report it says its not a factor and would only have to process the initial  part of the data stream to decide its not relevant.

I would also suggest that disabling a perfectly good Mode-S transponder would remove the advantage of providing ATC with your aircraft Callsign which aids them contacting you either on receiving a service or using a listening squawk.

But you are sending it in your E.S transmission.

But for  those that already have a Mode S that cannot send E.S, but want LPAT,  If you do not program a 24-bit address /hex or set it as “000000“ the Mode S transponder operates as a Mode A/C transponder only, but you would have your LPAT and  ES, to send your Callsign/Hex + Altitude etc.

[exfirepro]

I would also suggest that disabling a perfectly good Mode-S transponder would remove the advantage of providing ATC with your aircraft Callsign which aids them contacting you either on receiving a service or using a listening squawk.

I totally agree Alan.

But you are sending it in your E.S transmission.

That's correct John, but as NATS/ATC apparently can't receive ADS-B outside the south east of England, being able to get your call sign from your Mode 'S' transmission is essential for the listening squawk system to work properly throughout the rest of the U.K.! I had personal experience of this recently when passing below the TMA under Edinburgh's Base Leg and squawking the listening squawk, (while carrying out some PAW Mode 'S' tests). Edinburgh called me to confirm my max altitude and intended route when two ADS-B equipped airliners requested immediate descent above me due to severe icing on approach. Fortunately, thanks to PAW / SD I could see them coming so was already aware of the possible conflict as soon as I heard their request on the radio and was able to advise that I would stay below 2,000ft allowing Edinburgh to descend both airliners immediately to 3,000ft, both passing close above me on their approach. Unfortunately LPAT wouldn't have been much help here as presumably neither ATC or the CAT traffic would pick it up (assuming it runs SDA/SIL '0' as we have been told ADS-B with non-cert GPS has to).

Regards

Peter

[AlanB]

But you are sending it in your E.S transmission.

That's correct John, but as NATS/ATC apparently can't receive ADS-B outside the south east of England, being able to get your call sign from your Mode 'S' transmission is essential for the listening squawk system to work properly throughout the rest of the U.K.

Regards

Peter

Currently the ES element of the Mode-S transmission is not used by NATS in an Operation capacity in any location.

The Mode-S element sent in response to a ground interrogator contains two elements. The conventional A/C response with additional data fields on the end containing the Hex Code, Aircraft Id etc

The ES element of a Mode-S transponder is broadcast from the transponder and is a data message. The timing is set to ensure that the transponder response to a ground interrogator is not overlapped with an ES broadcast response.

If I may go back to the original issue regarding the use of two devices simultaneous transmitting the same aircraft id. We are both making individual interpretations of what we have heard and what is written. The ultimate deciding factors is the response from the CAA and if what has been published so far, or is in the public domain, is being interpreted differently then it needs clarification and I suggest that feed back to the CAA is necessary to sort this issue.